Jan Willem Petersen is an architect and researcher who graduated from the Architectural Association in London, having gained his diploma from the Gerrit Rietveld Academy in Amsterdam. In July 2005 he founded Specialist Operations.

"I think the terrorists have already won to a certain extent …. Without planting an actual bomb, they have forced everyone to think the unthinkable." Planning officer, Westminster Council, London, January 2005

Nothing seemed to function properly. Police ribbons blocked off many of the streets I normally took to get to the Architectural Association (AA) to pursue my research. My mobile phone rattled with text messages from friends and relatives. London was under attack. In physical terms, I was safe, but I could not shake off a sense of the bizarre. A few days before, I had completed my AA thesis on the city in relation to security and anti-terrorism policy. At that moment it felt strange, even embarrassing, to have intellectualised a realm now devastating the lives of those directly caught up in the events. A thesis had been given its reality-check.

The bombing attacks of 7 July 2005 in London destroyed or damaged the lives of many thousands of people. All who live, work and study in the city were affected – some in ways far below the level of conscious awareness. But the imprint of 7/7 on the lives of people not directly touched by the attacks is more than just personal or psychological.

All Londoners – as citizens, commuters, and residents – share the public spaces of London itself. These public spaces, especially in the central areas of the city, are increasingly subject to significant architectural changes designed to avert or minimise the threat of terrorist attack. The purpose may be justified in terms of protecting citizens; but the effect of many of these innovations is to monitor, channel and control the free movement of Londoners.

What happens to a city when much of its architecture and planning becomes subject to a political, counter-terrorist imperative? What is the impact on citizens of the securitisation of public space? Are these processes compatible with the life of the city as a healthy, confident civic space – one of the foundations of a modern democracy?

This article, which draws on my research into these issues, illustrates rather than attempts to answer these questions. In doing so, it seeks to emphasise that the political-architectural response to terrorism should also be a matter of public dialogue, debate and choice as well as administrative decision.

Jan Willem Petersen is an architect and researcher who graduated from the Architectural Association in London, having gained his diploma from the Gerrit Rietveld Academy in Amsterdam. In July 2005 he founded Specialist Operations

In recent years, partly under the impact of successive bombing campaigns by the Irish Republican Army (IRA) and its affiliates from the 1970s to the 1990s, British citizens have been asked to give up traditionally valued rights – freedom from intrusive security measures, a transparent and timely judicial process, for example – in exchange for better protection. If the government asserts that safety cannot be ensured without further infringements, then by implication the public domain – principally the city – will also be altered in ways previously considered completely unacceptable.

London, the principal target of the IRA campaigns as of the 7/7 bombers, has become an environment where the strategic use of space exercised by the state has become routine. The houses of parliament in Westminster, and the prime minister's residence in nearby Downing Street, have been provided with progressively tighter security in line with local and global events – from the IRA's mortar-bombing of Downing Street in February 1991 to the World Trade Centre attack in September 2001.

These measures have extended to almost all of Whitehall, London's political district. The restrictions of access here are particularly evident, but the creation and expansion of security zones around British governmental departments are visible at numerous other locations. They include a "ring of steel" around the City, London's financial district, imposed after two devastating IRA bombs in April 1993 and February 1996.

This permanent, urban-scale security structure has been complemented by a new breed of "temporary" security measures at key locations around London. They include arrangements to protect the United States embassy at Grosvenor Square. This building, the symbolic target of student and anti-war demonstrations from the Vietnam era, has seen several security upgrades (especially since the Beirut bombing of October 1983). The experience of 11 September 2001 opened a fresh phase, involving an expansion beyond the area around the embassy designated as "diplomatic space".

Today, a profusion of physical barriers surrounds the building, including a much-disputed concrete cordon. This barrier has been labelled "temporary", but as a former director-general of Britain's internal-security service MI5 told me: "Once a war on terrorism has been declared, who is to say when it is over? Once a weakness in security has been identified, it is unlikely any democratic government will dare to ignore it or to reverse measures taken."

The circumstances in which such architectural features are built are unclear; the architects responsible are required to operate in a legally ambiguous relationship with the legislation that regulates these features. This raises the question: can a single entity, even one of special status, make exclusive use of space previously in the public domain? Are the arguments of "exemption" and "unique circumstances" enough to justify such widespread development? In interviews with the planning department of Westminster council (which administers the area surrounding the US embassy), I was struck by the way that this leading London political authority was in practice powerless against the effective gutting of the legal framework guiding security-related architectural innovation.

A senior planning officer with the council told me: "The Americans are expanding their zone of influence and modelling it according to their own advantage … I don't think we ever approved a planning application (to build) these concrete blocks." On the relation of building and security, he said: "There is nothing in planning legislation or planning guidance that relates to security occasions. There is nothing specifically on anti-terrorism."

The paradox of security

The "force-protection" barriers at Grosvenor Square were placed to counter attacks by vehicles bearing conventional explosives. A close study revealed, however, that in some situations the US embassy would withstand a modest vehicle-borne explosion while the neighbouring Bahrainian high-commission building would be completely flattened. As significant, the barriers' very visibility is deemed by security agencies to have a strong deterrent effect. Thus, the embassy needs to broadcast its protective measures in order for them to be effective, radiating force and maximising visual presence. The arguments for security and for the projection of new, exclusive architectural features into public space are here linked.

The Vienna Convention of 1961 gives all diplomatic spaces a statutory right to protection. In Grosvenor Square this raises the question of equal treatment for the adjacent embassies and diplomatic spaces, whose protection on the level of the US embassy would force the closure of the square to the public. The extension of architectural forms of control also affects the living conditions and rights of residents of the square, many of whom have protested vigorously about these changes. Some residents sought the closure of their streets to the public out of fear of a potential attack on the US embassy building; they argued that their property would encounter the full impact of an explosive blast.

The experience of Grosvenor Square is only one manifestation of the architectural and urban aspects of the current security climate in London. It demonstrates that decisions taken in the name of security render many of the city's physical, social, economic and statutory mechanisms unsustainable; that, once taken, they are difficult to reverse; and that they no longer have an affinity with classic architectural practice.

What has happened in this single corner of London also raises the question of whether the "irreversible" character of security expansion and its spatial fallout can coexist with the very notion of a sustainable city.

It may be hard to imagine circumstances in which architects could instruct police forces on undertaking armed patrols. It is equally hard to see police forces and security services making valid judgments about the moment at which a security alteration becomes so extensive that city living is compromised. But this is indeed the predicament of London's citizens in the post-IRA, post-9/11 and post-7/7 era: submerged in the social and spatial ethics of the state.

I believe that architecture must be inspired by empathy and an ethic of social cohesion, and aim to benefit the urban public by contributing to the sustainability of their city. In this light, it is essential to register how changes in London's public buildings and spaces are implanting models of control and infringement that may undermine the free civic life, movement and communication that together compose one of the cornerstones of democracy.